Method of and machine for milling threads



Dec. 14 1926.

G. E. MIRFIELD METHOD 0F AND MACHINE FOR MILLING THREADS 1924 6 Sheets-Sheet 1 Filed Jan.. l1

Trae/)frs Dec. 14. 1926. 1,611,122

G. E. MlRFlELD METHOD OF AND MACHINE FOR MILLING THREADS i Filed Jan. 1l, 1924 6 Sheets-Sheet j T ,Jaa 140,143

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Dec. 14 1926.

G. E. MIRFIELD METHOD OF AND MACHINE FOR MILLING THREADS Filed Jan. 11. 1924 6 Sheets-Sheet 5 Dec. 14, 1926.

G. E. MIRFIELD METHOD OF AND MACHINE FOR MILLING THREADS Filed Jan. l1, 1924 6 Sheets-Sheet 4 Dec. 14. 1926.. 1,611,122

5. E. MIRFIELB METHOD 0F AND MACHINE FOR MILLING THREADS Filed Jan. ll, -1924 HTTORNEYS Dec. 14 1926.

G. E. MIRFIELD METHOD 0F AND MACHINE FOR MILLING THREADS Filed Jan. 11. 1924 6 SheetsfSheet 6 Patented Dec. 14, 1926.

GEORGE n. MIRFIELD, or YoUNos'roWN, omo.

METHOD OF AND ,MACHINE FOR MILLING THREADS.

Application tiled January 11, 1924. Serial No. 685,545.

My invention is particularly adapted for the formation of threads on the ends of pipes and tubes and I will more especially refer herein to its employment for that purpose, it being, however, understood that the invention is capable of adaptation to and employment for other purposes as well, such as the milling of threads on the ends of rods or other work of like character. Y

A principal object of my invention, is to provide a novel method of milling threads on pipe or other classes of work and, additionally, to provide a machine adapted for the performance of the said method whereby smooth and accurate threads, either straight or tapered, may be produced with a minimum expenditure of time and labor and within the tolerances and of the standard required in modern machine shop practice. Further objects, features and characteristics comprehended by my invention will hereinafter more fully appear.

In accordance 'with the principles ofnmy invention and Vin the `practice of my im '5 proved method I employ a plurality, con-l veniently a pair, of rotatable milling cut` ters respectively of suitable characters to impart to the work a roughing cut of suilicient depth to remove the scale and true the surface which is t0 be Athreaded and to form the desired threads thereon,` and so arrange these cutters in their relation to each other and to the work that the roughing cutter shall operate on' the rotating work at a oint in advance-of that at which the thread ing cutter operates. thereon, with the result that the threading' cutter is relieved from the duties of penetrating the scale and truing thework and relegated Ato theV sole duty of cutting into the clean metal exposed by the roughing cutter for a depth suliicient to form the required threads` thereby contributing to the accuracy of their formation and materially enhancing the life of thc r cutter.

Moreover, for the production of tapered threads I utilize cutters of tapered form,

that is. tapered longitudinally with respect y to their axes of rotation in conformity with the taper of the thread which it is desired to produce and of substantially the lenarth of such threads, and provide the threading cutter with a plurality of annular teeth having the profile of the form of the desired thread but without pitch so that by effecting substantially a single revolution of the work with respect to this cutter and simultaneousy moving the Work longitudinally for a istance substantially equal to the pitch of the thread to be cut, While effecting slight relative movement between the work and the cut- `ter in a direction substantially normal to the axis of the latter, a complete tapered, ac curate s iial thread of the desired length will be ormed on the work.

lVhile in carrying out my im roved metho d and for the purpose of e ecting these several results various means may be employed, it. is an object of the present invention, as hitherto stated, to provide a suitable machine for that purpose which, in its preferred embodiment, comprises among other things novel means for effecting the requisite relative longitudinal movement between the work and the threading. cutter necessary for the production of a continuous spiral thread when employing a cutter having form teeth without pitch; separate roughing and threading cutters and means for supporting both cutters in a manner to avoid disalignment or looseness thereof with consequent chattering and resulting imperfection in the work; means for automatically feeding the rougliing cutter to the de sired depth in the work and for thereafter maintaining a fixed relation between the ,axis of the work and the axis of the cutter so that in the cycle of operations requisite for the' production of the thread in the Work any given point on the latter will be subjected to the action of the roughing cut ter prior to that of the threading cutter; means for bringing the threading cutter into proper engagement with the Work after the roughing cutter has traversed a limited p0rtion thereof and rendered it suitable for the reception of the threading cutter; means for suitably chu'ckingand centering the Work and for imparting rotation thereto; means for eil'ecting a gradual relative movement between the threading cutter and the work in a direction substantially transverse to the longitudinal axis of the latter to thereby enable the production of accurate tapered threads by adequately compensating for the difference in radial magnitude of diii'erent portions of the complete thread, as well as the provision of improved means for effect-- los ing the return of certain of the parts to initial or starting position following the completion of the threading of one piece of -work to thereby place the ma'chine in condition for thereception of theffollowing/ piece.

Thilo a machine adapted for the performance of my improved method and embodying such of the means to Which reference has just been made as may be desired, as well as other adjunctive means and instrumentalities requisite or desirable for their proper coordination and operation, may partake of many forms, a convenient manner of pro-v viding such a machine is to operatively combine suitable means and mechanism with a standard milling machine, thereby producing an organized, operative unit embodying such novel features and characteristics as will hereinafter more fully appear. Therefore. to enable those skilled in the art to comprehend and practise my invention, I have illustrated in \the accompanying drawings and will now proceed to describe a machine of that general character and Will also eX- plain its use and method of operation in forming tapered threads in accordance with the preferred practice of my improved method` lt will, however. be understood that other means and instrumentalities than those now to be described may be employed if desired in the performance of my said method and that in consequence the practice thereof is not confined or limited to the use of any specific mechanism, and further, that While the particular machine herein illustrated and described is well adapted for the efficient and economical practice of the said method the same may be readily modified with respect to design, construction and arrangement of the several elements entering thereinto as may be desired.

As milling machines capable of adaptation to the purposes of my invention as aforesaid are well known to persons skilled in the art and as the specific form and details of construction of the precise machine employed are. save in certain particulars, immaterial, in the accompanying drawings I have illustratcd thel principal elements of such a milling machine in a more or less conventional way and it will therefore be understood that any suitable milling machine such as may be readily purchased in the open market and comprising a movable bed or table with means for vertical and transverse adjustment thereof and preferably having an automatic longtiudinal feed for the table and a quick return feed therefor may be utilized. Additionally. I prefer a machine having an overhanging arm arranged to provide a bearing for the outer end of the cutter arbor since in machines of that general construction any tendency of the cutter arbor to whip or spring is prevented and the accurate runmngof the cutter consequently assured.

Referring now more particularly to the drawings, Fig. 1 is an end View of the organized machine in its preferred embodiment, the same being shown with the parts in initial or starting position as at the commencement of the threading operation on the work, which is also shown, and Fig. 2 is a rear view of the machine shown in Fig. 1. Figi?) is a somewhat enlarged side elevation of certain of the mechanism removed from the machine table, and Fig. 4 is a similar view of the op-posite side thereof, the parts being shown in the same position as in Fig. l and broken away into vertical section at certain points to better illustrate internal construction. Fig. 5 is a further enlarged top plan view with certain parts in horizontal. section of certain of the mechanism in operative position on the machine table; Fig. 6 i5 asimilar, partially fragmentary View thereof but removed from the table and with all parts shown in plan; Fig. 7 is a fragmentary vertical section on` line 7-7 in Fig. 6; Fig. 8 is a further enlarged fragmentary view partially in section and partially in elevation ot' the main' spindle and adjacent parts in one position; Fig. 9 is a similar view, but Wholly in central section, of the same parts in a different position and additionally illustrating the internal construction of a preferred form of chuck which may be employed when the Work to be threaded is a pipe or other hollow object, While Fig. 10 is a transverse section on'line 10-10 in Fig. 9, Fig. 11 is a fragmentary plan view illustrating the operation of certain of the mechanism employed to eifect the return of the main spindle to initial position after the completion of the threading c vcle; Figs. 12 to 12t inclusive are diagrammatic figures consecutively illustrating the relation of the cutters and the Work at different periods during the threading cycle, and Fig. 13 is a diagrammatic view illustrating on an exaggerated scale the relativeangular disposition'of the axis of rotation of the threading cutter and the axis of the main `spindle when the machine is intended for the production of tapered threads. Similar symbols are used to designate the same parts in the several figures.

At this point it will be of advantage to briefly refer to the sequence of steps and the relative positions assumed thc cutters and the Work during the'series of operations performed in the threading of a piece of Work or during the threading cycle as it may conveniently be `termedas by so doing a more ready and adequate comprehension of the construction of the variuos parts of the machine and their method of operation as hereinafter described will be attained.

Assuming that a formed upon one end of a pipe P, the end of the pipe to be threaded is first chucked,

'taper thread is to be' centered and clamped to the main spindle of the machine so as to move in ,correspondence therewith. Above this spindle but out of vertical alignment therewith the threading cutter T is supported on the main arbor of the machine so as to be,dri.ven thereby, while adjacent but out ofcontact with the pipe, below the threading cutter and also out of vertical alignment therewith, isdisposed the roughing cutter R.` Preferably both of these cutters are similarly tapered longitudi-i nally and in the same directioniin correspondence with the taper of the thread which it is desired to form, and whilejt'he threading cutter is provided with a plurality lar form teeth without pitch as hitherto described the roughing cutter is provided with longitudinally extending teeth of any Suitable form for effecting a roughing cut on the pipe to remove the scale therefrom and bring the pipe t9 truly circular cross section. The parts being disposed in the manner aforesaid, the pipe and both cutters. are caused direction, the pipe at relativelyA slow speed and the cutters at relatively high speed, and

' threads, which With this the roughing cutter is moved horizontally toward the. pipe for a Suiicient distance to cause it to enter the pipe for the requisite depth to produce the desired roughing cut and thereafter maintained in that position until it has traversed the entire surface which is to be threaded. As the pipe continues to turn with respect to this cutter, the point where the 'cutter first entered the pipe, or in other words, the point where the roughing cut initially commenced, gradually moves around and upward toward the threading cutter and simultaneously movement both the pipe and the roughing cutter, while maintainin their relative position. are gradually move horizontally in a direction to cause the pipe to approach the threading cutter in a generally tangential, as distinguished from a radial, direction until the cutter enters the pipe to a depth requisite to form the will ordinarily be accomplished when the pipe and cutter are in Substantial vertical axial alignment. When this oint isreached, further movement of trans ation of the pipe and roughing cutter is arrested and thereafter the threading cutter .and the pipe remain in the same relative position until that portion of the ipe which is' to be threaded has been comp etely subjected to the action of that cutter, thus completinghe threading cycle. Moreover, during the operation of the/threading cutter on the pipe, the latter is given a longitudinal movement with respect thereto at a-predetermined rate-of progression and is also given a gradual' and ver. slight movement in a direction substantia ly transverse to the axis of rotation of the cutter to eiect the neces- Apered thread which of annu? to rotate, preferably all yin the samey sary, compensation for the dili'erence in radial magnitude of different points on the tais in process of formation, these several combined movements and different steps and operations 'resulting in theproduction on the pipe of a continuous spiral tapered thread of a form similar to the profile of the teeth on the threading cutter. Thel machine which I prefer to employ for their accomplishment and to which reference has hitherto been made in a general Way will now be described with greater particularity, reference being had to the accompanying drawings.

As shown, the machine comprises a base 1 from which rises ay pedestal 2 to the upper extremity of which is rigidly secured an overhanging arm 3 the free end of which extends over the movable table or bed 4. This arm is providedwith a depending bracket 5, slidable on ways 6 on the under side of the arm, in the lower end of which is journaled theV outer end of the arbor 7 which, through suitable mechanism (not shown) is arranged to' be driven yfrom the main shaft 8 which may be provided with a pulley 9 for the reception of a belt extending to the source of power employed. `If desired, however, the machine may be supplied with a motor drive or other means for effecting rotationiof the shaft 8. The bed 4 which 1s provided with wa s 4 on its under side, is longitudinally sli able in a -block 10 in a direction at right angles to the axis of lthe arbor 7 while the block is transversely adjustable, that is, in a directiony parallel to said axis on ways 10 formed on a supporting bracket l1 which in turn is carried by and vertically adjustable on ways 11 disposed on the face of the pedestal 2 and which may also be supported adjacent its opposite or outer end on a threaded vertically adjustable column 12 carried in a housing 12 rising from the base. It will be understood that the machine is provided with suitable means (not shown) for effecting vertical adjustment of the bracket 11 and justment of the block 10 in the manner common to milling machines so that the bed may be moved both vertical] and longitudinally with respect to the 'ardor 7 in the initial setting of the machine. Additionally, the bed itself is provided with means-for reciprocating it beneath the arbor, saidn means preferably comprising an automatic feed for moving the bed rearwardly or to' the right when viewed as in Fig. 1 and a quick return feed, convenientl operated, for moving it `forwardv y or to the left when viewed as m said iigure, this latterV means being operable through the hand Wheel 13 in the ordinary manner.' For throwing the automatic feed in or out, the, machine may also be provided with a tri 14 which, when moved to the left from the cross admanually y the opposite direction from the position.

which it assumes when the feed is so ein gaged, is effective to throw out the feed and thereby arrest the rearward movement ot' the ,j

table. As the dilferent features to which reference has hitherto been briefly made are generally embodied in ordinary milling niachines and, together with the mechanism employed for accomplishing them, are well known and understood, further description thereof is unnecessary to an adequate comprehension'of the present invention.

Upon the table 4 of the machine I dispose mechanism in the nature of a fixture or attachment whichy more particularly may comprise a base 2() held down by bolts 21 or in any other suitable way. This base is of substantially elongated rectangular form and more orV less adjacent its center is provided with undercut Ways 22 extending enerally parallel to the side edges of the ase and in which is slidabl mounted the roughing cutter supporting lock 23 hereinafter described. In front of the block, that is, more nearly `adjacent the front edge of the base, the latter is provided with a vertically extending housing 24 in which is journaled the main spindle 25, while projecting from the side of the base most nearly adjacent the pedestal 2 when the base is on the table are longitudinally separated brackets 26 forming supports for the drive shaft 27 which is rotatably journaled therein and extends generally parallel to the base, while on its opposite side the base may be provided with longitudinally spaced brackets 28 through which is slidably extended the feed trip rod 29 hereinafter: more particularly described.`

For supporting the roughing cutter R the roughing cutter supporting block 23 is provided with a forwardly extending bracket 30 which may be integral with the block and in which is journaled the roughing cutter shaft 31 on which is removably clamped the rouvfhinor cutter in an suitable w`a conveniently by a clamping nut 33. In order to prevent any springing or whipping of the shaft the outer or overhanging end is journaled in a support 34 carried by a bracket 35 bolted or otherwisesecured to the roughing cutter supporting block as by bolts 36. In order to permit the ready removal of the support 34 when the cutter is being changed. 1 may rovide the bracket with Ways 35 over which the support is adapted to engage so that the latter may be readily slipped olf of the bracket when it is desired to clear the end of the shaft and as readily returned to position thereon. It will thus be observed that under operative conditions the roughing cutter shaft is securely supported on both sides of the cutter and the latter thereby constrained to run truly under all conditions.

The roulghing cutter supporting block is also provi ed with a rearwardly extending tongue 37 at the extremity of which is mounted a cam roller 38 adapted for cooperation with a. horizontally disposed cam 39 rotatably mounted on a vertically extending pivot 40 carried by the rear end of the bed. To enable adjustment of the block toward or away from the cam I prefer to arrange the tongue to slidably extend into a slot 41 in the block and to provide for its longitudinal adjustment in this slot by means of an adjusting screw 42 which extends through the tongue and has its forward end threaded into the block. The rear end of this screw projects through the tongue and is provided with an adjusting collar 43 carrying an indexing dial 44, the parts being arranged in such manner that by turning the collar the screw may be screwed in or out in the block with corresponding movement of the tongue' with respect thereto, a set screw 42 extending downwardly through the block to contact with the screw 42 being employed to lock the latter in any desired position of adjustment. This capacity for relative adjustment between the ton ue and the block is of utility in regulating t e depth of the roughing cut as will hereinafter appear.

The drive of the roughing cutter is effected, as hereinafter more fully described, through the medium of a gear 45 mounted on the rou'ghing cutter shaft which also carries another gear 46 meshing with still another gear 47 carried by a stub shaft 48 journaled in the block and extendin through an arm 49 projecting from the si e thereof. On the outer end of this shaft is mounted a worm 50 meshing with a worm gear 5l splined upon the main shaft 27 so as to be capable of sliding movement thereon but constrained to rotate therewith. As during the operation of the machine the rougliing cutter supporting block is moved back and forth in the ways 22, it is necessary in order to maintain constant and pro er engagement between the worm 50 an gear 51 to provide means for moving the latter on the shaft in correspondence with the movements of the block, a result which can be conveniently accomplished by securing the gear to onejend of a flanged sleeve 52 which is engaged by a fork 53 disposed at the end of a short overhanging arm 54 extending from the arm 49 in such manner that while the sleeve can rotate in the fork in correspondence with the rotation of the driveV shaft, any movement of the roughing cutter block in a direction parallel to the shaft will elfect a corresponding ,slidingk movement of the sleeve and gear thereon. Thus, irrespective of the position of the block, the worm 50 llll narines and gear 51 are constantly maintained in i proper meshing engagement and the gear constrained to Vrotate with the shaft and actuate the worin. The means employed for driving the gear are hereafter more fully described.

Bought/ng .cutter translating means. 4

The 'main shaft is also 4employed for effecting rotation of the cam 39 which, among other things, is 'operative to advance and retract the rou'hing cutter block through the medium of t 1e ton e 37, and to this end the shaft `27 is provi ed near its rearmost extremity with a worm dis osed in mesh- --ing engagement with a horizontally positioned worin gear 56 carried by a short stud rotatably supported on the base 20. Above this gear and von the saine stud is mounted at the proper time in the cycle of operations, to hold the block in such position while the roughing cutter is operatin o'n the work, and to retract the block lto initial osition after the roughing cutter has comp eted its operation on .the work,.and the cam may therefore be of. any construction suitable for accomplishing these lresults. I n the particular embodiment shown the cam comprises a circular horizontal] disposed plate to the rim 'of which is bo teda short deending segment 60 cut away on its inner iace as at 60 to the desiredcontour and a hub 6l ofsuitable contour arranged beneath the plate in the plane of the depending portion of the segment, thus providing a cam groove 62 between the segment. and the hub .of suitable width to accommodate the cam roll.38. When the cam is so constructed the hub is operative during the rotation of the`cam to move the roll forwardly atthc proper time and to hold it in advanced position for the required period, and the se ment is operative to thereafter retract the rol and hold it in retracted position; it is therefore unnecessary to provide-a continuous clgsed cam groove either'by extending the segment entirely around the (plnte'or by routing outa. groove in the un er surface thereof. l l r The cam is also provided with a dog .68 which `projects beyond its periphery and is convenientl cam for a imited distance. This dog is f such form that at the proper point in the rotation of the cam it will contact with the preferably beveled end of a vertically prowill sli adjustable with respect to the@ jet-.ting linger 64 adjustably mounted upon andnear the end of the trip rod 2i) to extend in the path of the dog, so as to ur e the rod forward against the resistance of t e spring 65 disposed about the rod and cause '70 it to en age the free end ofthe trip 14 n thereby 4 orcing the trip/to a position to throw in the'automatic feed for the table or bed 4, the conformation of the contacting.,

surfaces of the dog and of the finger being "Hil such that after this result is accomplishe the dog as the cam continues its rotation,

(le free of the end of the finger.

Main spindle.

In operation the requisite rotation ofthe pipe' or other work is ei'ected from the referably hollovir main spindle 25 to whic the pipe is suitably centered and clam ed and the construction of the spindle an certain adjacent mechanism will now be described. The spindle itself is disposed above the base 20 and generally transversely thereof be- 'tween the forward edge 20 of the base and the roughing cutter and is journaled for iro-` tation in the housing24 preferably throu"h the medium .of an adjustable tapered s it collet bushing 70 whose position is contro by an adjusting rin 71 in the usualmanner so that accurate adjustment of the'bushinv may be made when required to com nsat for wear. At its inner end the spin le may be provided with'an enlarged integrall annular head 72 which is in turn supported for rotation in a similar adjustable bushing 7310(1 controlled by an adjusting ring7 5 and disosed in a housing .74: integral with and ris# ing from the base. The interior of the head is cupped out togenerally s herical contour to receive a centering ball tained in position in the head by a colla-r 7 7 having a spherical inner surface and removably `secured in a. depression in the forward side ofthe head by screws 78, the arrange- 6 which is i'e- 105 ment being such that the centering bgll is 110 very snugly seated in the end of the spindle but is capable of limited universal movement with respect thereto. To constrain the ball to rotate with the spindle a stud 79 is extendedthroughthe head to project in to a slot 80 formed in the ball while removably disposed Iin a tapered boi-e in the centerfcf the ball and projecting therefrom is a center 81 which may be of ordinary construction. The ball is also provided with an an 12 nulai' preferably integral flange 82 which projects therefrom in a direction away from the lead 72 and surrounds the centering point of the center 8l. This flange forms a compnent part of the means Aemployed for operatively securing the pipe to the spindle and which will now be described.

Pipe clnwkz'ng,rimterng, mul dw'ag'ng means.

pipe any suitable means may be utilized, I prefer to employ a chuck yof the general character of that disclosed in my pending l 1s sprung or distorted by the chuck or other 'acter in my improved machine hol infr means employed and the threads formed uponit while vso distorted, the pipe will to some extent "resume its original torm after the gri of the ,chuck is released, so that althoug the threaded area may have presented a truly circularV cross sectionafter the threads have been formed but'beforethe release of the chuck, it thereafter presents a more or less elliptical cross section.`

I have therefore illustrated and, as stated, prefer to employ a chuck of the general character of that disclosed in my sai application designed for disposition in the interior of the end of the 1pc, and which may comprise a plurality of alls 85 disposed in a generally cylindr1cal carrier 86 and opera,- tive to 'force radially outward against the pipe wall a plurality of blades 87 when a central generally corneal member 88 is moved into the carrier in a direction to force the balls outwardly away from the center. As shown, this member has at its larger end. a threaded region 89 extending through a cor-v respondingly inteially threaded bore in the carrier; thus by rasping the nose or smaller end of the mem er'wlnch rojects beyond the opposite end of the earner with a suitable wrench and rotating the member in the proper direction, the balls may be crowded together so as to force the blades outwardly to en age the pipe with equal pressure at a plura ity of spaced points, thereby securely clampin the chuck in the interior of the pipe wit out any distortion of the latter. As the chuck forms no part of the present invention save as' it is utilized forthe urpose of holding the pipe in the thrca ing IVhen using a chuck f this eneral charprovide the nose of the member 88 with a central de ression90 adapted to receive the point' o the' center 81 as well as an annular oove 91ex tending around the nose and the side -of which ad'acent the end of thefi'iose maybe suitably inclined. This ove is adapted to receive the correspondingly beveled ends gf a -pair of spring pressedpins 92 extendmg inwardly at diametrically opposed oints -throu h the annular flange 82 an Ysur, roun ed by a rotatable collar 4disposed operation, further description thereohere` 1,e11,1aa

thcreabout between a shoulder 94 on the Y flange and a covering plate 95 secured to the wardly Aagainst the resistance of the springsl when the collar is rotated. Thus, by rotating the collar in one" direction the pins .can be caused to withdraw from the spacey within the flange 82 to permit the nose of the member 88 to be entered therein,`the chuck of course having been previously seated in andclamped tothe pipe,'after which by rotatmg the collar in the other direction, the

pins may be caused to progressively enter the groove 91 and` by"coactlon with the beveled sides thereof to" draw the-nose ofi the member 88 against `the point f the center 81 and firmly ratelycentering the` chuck and in turn the pipe and lockin it in, such centered position, and for eficting rotation of the-pi e in correspondence with the rotation of tlie spindle, the cover plate 95 is provided withv an outwardly projecting dog 98 ada ted td enter between, any two of a plura ity of clamp 'it'thereto, thus accuspaced lugs 99 with which the end of the carrier is provided. d Y

Main spindle animating ncm.

i l 10u The rotation of the main vspindle 25 is e'ected through the mediumof a. worm gear 100 disposed 1n meshing enga ement with a worm 101, on the-forward en drive shaft 2T. -.This ar is provided with an inte ral hub` 102 avin'g-a peripheral grooveY or rece tion.v of a fork-103formed at the end of a racket 104 integral with the base, and is'splined to the spindle b a key Vor spline l10560 as to rotate therewit while permitting the -spindle'to slide longitudinally throughthe ar. Thus, irrespective of any 'longltudina v'movement lof the spind1ethe gear by reasonof its being supported from the'jork is'constantly maintained in mesh with the worm and adapted to rotate the spindle in correspgndenee with the rotation offthe drive sha Y Durin the threading cycle as hitherto stated, t1e"` spindle and in turnthe pipe is moved longitudinally for a sullicient dis- Atance to produce, c thread of the desired pitch-upon the pipe. and for ell'ecting this ,result Iemploy novel 'means now to be described. Hitherto in threadiig machines emb dymg provision for e ecting longitu inal movement of the work with, respect to lthe cutter witha view to producing a spiral 'of the main.

lili) lative rotation between the spindle and the nut. is effective to move the spindle longitudinally,

assuming the nut to be sta'tionarily supported, -at a rate of linear progres-- siondirectly corresponding to the pitch of the thread. Under theseconditions a single the thread to be formeV f `relative revolution of the s indle with re'- spect to the nut is thus effective to move the spindle longitudinally for a distance equal to the pitch of thel thread, that is, if the mas.- ter thread on the spindle'is of ten pitch or ten threads to the meh, a single revolution of the spindle results in moving the latter longitudmally for one-tenth of aninch.

This method of moving the spindle is openv to thedisadvantage that in case the master thread is not entirely perfect, the error transmitted to the spindle is not erely the error in a single convolution 'of 4he master thread but the sum of the errors 'of all the convolutions thereof. tFor example, if the error in each @convolution of the master thread is .001 and the thread is of ten pitch to the inch, the error in the longitudinal movement of the spindle produced by a nut will be ten times .001" or .01 instead of merely .001, a conditionV which is inimical to the production of accurate tlireads in the work. n

In accordance with my invention, however, this ditculty is obviated by providing the spindle with a master thread o greater pitch than the thread to be formed 1n the work and then effecting the requisite longitudinal movement of the spindleby a partial relative revolution between it and the nut in- .stead of by a complete revolution.v Thus, for example, if the master thread be formed with a-pltch of one to the vinch and it be desired to form a thread of ten pitch to the inch, the requisite longitudinal movement of the spindle may he effected by causing a relative revolutlon betweenethe nut and the spindle of only one-tenth of a complete turn,

so that instead of the sum of all the -errors in the master threadbeing communicated to the. spindle but one-tenth of such sum is communicated thereto. The utilization of a master thread of greater also results in a minimizationl of error in the latter for the 'additional reason that, as a practical matter, amaster thread of such character, the convolu'tions or se ents of which are ordinarily of relatively great cross-sectional area, can be machined more accurately than the-ner master threads hitherto employed and is subject to `less wear under operative conditions by reason of the ater area of l contact between the relative y lmoving surs indle isV in the" ingly internall single relative revolution between it and the itch than that of.

faces of the thread on the spindle and in the nut, so that their accuracy of such master threads is ordinarily initially greater and canbe preservedfory a much longer period ofrtime with corres onding resulting accuraply'in the threads ormed by Vthe machine.

n accordance `with these principles I therefore provide the spindle25 with an external master thread 110 of greater pitch than the thread which I desire to form on the ipe, for example, a pitch of one thread e inch when it is desired to form a ten pitch thread. 'This thread I dispose on the spindle in the -rear of the head 72 .con-

veniently enlarging the diameter of the s dle at this point for its rece tion and .o ereby providing asmall shoul er 111 at the rear end o-f the thread which is ladapted n to abut the face' of the .housing 24 when the osition shown in Fig. 8.

histhread`whic1 may' be either single or multipleyis cooperative 'with a corres ondthreaded nut 112 positioned between the a jacent end faces of the housings 24 and 74 so as to beincapable of movement in a direction parallel toits axis a1- thoughv free for rotation about the spindle.

and integral with this nut or rigidly secured thereto is a gear 113 in meshing engagement withl asimilar gear 114 keyed to a sleeve 115 journaled for rotation ina lweh 116 which extends vertically upward from and is integral with the h Thegear- 114is disposed between .the face of the web and'fthe ratchet collar 117 also keyedto the sleevev and provided withaxe 20 .and witlrthe housing peripheral ratchet teeth 117', while adj acentV I thel collar and pivotally mounted for-rota tion on. the sleeve'is a' pawl 'arm' 118 provided with a spring pressed pawl 1.19l ada ted:for engagement with vthe ratchet tc'et the free end of the arm extendingin a generally' downward direction "from Vthe sleeve. 4Upon the opposite side of the web and also keyed 'to the sleeve'is a clutch member 120 having clutch teeth 120 on itsend face ada ted for coo erativc engagement with simi anteeth ont e end face of a gear 121, which' may be'l mounted 'forA rotation uponone end of-a plunger shaft 122 ex@ tended through sleeve 115 andsurrounded at itsother end y a coil lspring 123 maintained 1n positionby nuts l124 in such manner that the sprin tends to maintain lin mesh lthe clutch tee rotation therewith in the gear 100,.and the face of gear 121 is made of somewhat greater width. than the ment so that the .gear is locked to the c u member to rotate the latter, or are raised' on the gear yandon the clutch' member. The gear'1214 is. in meshing en- 'l gagement with a gear -125 splined to .the 'spindle for lidng movement thereon and a Vmanner similar to out of engagement with said teeth as when the clutch is being rotated independently of the gear as hereinafter described, gears 121 and 125 will remain constantly in mesh.

The clutch teeth on `the clutch .member and the gear 121 are so designed that when engaged, as shown in the drawings, gear 125 is effective to drive gear l1,21 in the direction indicated by the arrow, thusdrivin'g nut 112, through sleeve. 115,`gear 114 and ear 113, in the same directionas that in ich the s indle is rotated by gear 100 in the threa ing operation.

It is, however, important that the speed of rotation of the nut Vshall bear a certain definite relation to that of the spindle in order that the linear progression .of the latter shall bear the proper ratio to the movement of rotation thereof so that for each com plete revolution of the spindle, and in turn the work, the work will be -inoved longitudinally of the cutter `for a distance equal to the pitch of the thread to be formed. In other words, assuminga thread bf ten pitch to the inch is desired and that the master threadis one pitch to the inch, it is necessary to move the work longitudinally of the wit thread tobe clito` .cutter for one-tenth of an inch for each revolution of the work, and it is therefore necessary to design the ratio of the gears in the train through which the nut is driven with this end in view. Thus, in the example given, the gear 125 may be rovided with 54 Vteeth, gear 121 with 60 teet and both gears 114 and 113 with any similar number of teeth such as 57`- Under ese `conditions it will be apparent that for each com lete revolution of the spindle the nut will e turned for nine-tenths of a revolutioiror through an angle of 324, with the rresult that the spindle will be moved'through the nut for one-tenth of an inch, that is, forrone-tenth of the itch of the master thread. It will of coursexe understood that othergear ratios nia be employed to effect the'same result il a-master thread of 'similar pitch and Jfurther that with a master thread of different' pitchit will ordinarily be necessary to utilize caring of stillother ratios, the ultimate o `ject `to be attained in any case beirfg to eiect through a partial revolution of the nut rior each complete revolution Aof the spindle,` alongitudinal movement of the latter for a distance equal t the pitchi ofthe pin retuifniy 'marinai f ing position, as shown in VAFigli,-totinal position, substantially Za-iislirmn in Fi"g,"9, suitable means for returni the s indletogs'tarting position are provid 'le means may be ofg'any convenientkform, Vit"ils,"how c ever, of extreme importance that they be of a character to effect positive en agement of the shoulder 111 with the face o housing 24 each time that the spindle is returned so as to always bring the spindle to rest in exactl'y the same position and thus insure that the forward movement of the spindle will be always initiated from exactly the saine point for each threading cycle with resulting ac.-

.curac vdu on consecutive pieces of work,l irrespective of any slight wear or looseness between the parts' of the spindle actuating mechanism.

For attaining this result themeans which I prefer to use comprise a link 127 pivoted to the free end of the Eawl arm 118 and to one end of a Horizonte y movable lever 128 pivoted at its other end on a stud '129 carried by the base. This lever may be provided near its pivoted end with an eye A130 in which is arran ed a perforated block 131 through which slidably extends a rod 132 surrounded by a coil spring 133 and attached to which is one end of another sprin 134 having its other end secured to an suitable point on the base. The position o the lever under the influence of spring 134 is normally such that the end ofthe ratchet arm extends generally toward the rear of the machine, and from this position the lever may, be swung forward by the action of a trigger 135 pivoted near its center td the base,and having one end pivoted to the rod and the other extending over the edge of the base for actuation by a stop` 136 which Niiay be secured to the main pedestal 2` the and similarity in the threads pro" veral parte being so designed that when the table moves to the rear the trigger will slide over the stop without actuating lever 128, but when the table is drawn forward the trigger will engage the stop and swing the lever in a similar direction, thus/caus-V lll) arm118 rotates sleeve 115 in a direction opposite to that in which the clutch teeth are designed to lock the clutch member and gear v 121 to ether, the teeth on the member ride Since in thepitoi fthelmecline andi in the mannerjnshdeseribed,,the'spindle is caused to move toward therightrfm starts.

over o se. n the gear, shaft 122 sliding longitudine lyin'the ysleeve against the resistance of spring 128 for asuicient distance to ermit such relative movement of the teet fbut being immediately moved by the sprin to a position'to again sleeve is completed.

lock the teeth toget er as s0011- as the rotation of the It will thus be apparent that rotation of the gear 114 through the movement imparted to the sleeve by the pawl arm is operative to rotate nut 112 in the same direction as that in which it Was rotated when the spindle was advancing, and as the nut is prevented from longitudinal movement through its engagement with housings 24 and 74 the result of its rotation is to return the spindle toward its starting position until shoulder 111 contacts with the face of the housing 24- and thus prevents further movement of the spindle in the return direction, during which, of course, the spindle has slid longitudinally through gears 100 and 125.

As it would be practically impossible to design and operate the various parts so that the forward movement of the pawl arm Would be arrested simultaneously with the movement of the spindle, I prefer to provide at some point in the linkage through Which the pawl arm is actuated, a suitable yielding connection such as is effected in the present instance through the medium of the spring controlled rod 132, so that when the sleeve has been rotated by the paWl arm for a sufficient distance to return the spindle to starting position and further rotation of the sleeve thus prevented, the yielding connection in the linkage can take up any further motion imparted from the trigger 135 Without injury to the parts by the rod 132 sliding through the block 131 against the resistance of spring 133 until the trigger passes the stop 13G. after which springs 133 and 134 operate to pull the lever 128 rearward and in turn swing the pawl arm in a similar direction to its normal position substantially as shown in Fig. 1, the pawl119 during this movement merely riding over the ratchet teeth Without imparting any movement thereto.

Maz'nsliaft driving means.

It will have been observed that the main spindle and cam 39 are driven from the main shaft 27, and this shaft in turn may be preferably driven from the roughing cutter shaft and the latter from the main arbor 7 through the medium of a gear 140 mounted on the arbor 7 and which meshes with a floating idler gear 141 in turn meshing with the gear 45 carried by the roughing cutter shaft. The idler gear is supported by a pair of spaced links 143 each pivoted at one end on the main arbor and at the other on a short shaft or stud 144 on which the idler turns and from which another pair of substantially similar links 145 depend andare in turn pivotally mounted at their ends on the stud and on the roughing cutter shaft. Thus, the idler is always maintained in mesh with both gears 140 and 45 irrespective of the position to which either the roughing cutter shaft or the table 4 may be brought by reason of their respectivemovements of reciprocation in the oper'ation of the machine, and it will be apparent that rotation of the arbor 7 will be operative to drive the main shaft 27 through the train comprising gears 140, 141, 45, 46, 47, Worm 50 and worm gear 5l, and further that when the arbor 7 is stationary the drive shaft27 Will be prevented from rotation and, in turn, the main spindle, roughing cutter shaft and cam 39 through the lockin action exerted by the several worms an worm gears through which the drive of these several elements is eifected.

Angular disposition of main spindle.

In a tapered thread the radial distance from the axis of the piece to similar points on diii'erent thread segments varies in accordance with the taper; thus, the distance, or radial magnitude as it may conveniently be termed, from the tops or apices, for example, of two adjacent thread segments to the axis of the piece is .slightly different though measured in the same radial plane. It is therefore necessary in milling such threads to provide means for imparting to the cutter or the work, simultaneously with their relative longitudinal and rotative movements, a very gradual and slight movement generally transverse to the axis of the Work so as to compensate for this difference in radial magnitude by progressively causing the cutter to take a slightly deeper or lighter cutin accordance with the direction in which the relative longitudinal movement of the cutter and the work is effected, as in the absence of such transverse movement the cutter, upon completion of a single complete circuit of the surface of the Work, would thereafter either cut into the threads already formed or else not be effective to cut a full thread on the ensuing circuit. This compensation I prefer to effect by inclining the longitudinal axis of the spindle so as to parallel the taper of the threading cutter instead of mounting the spindle on the base 20 with its axis parallel to the axis of the arbor 7, but since, under ordinary cond tions, such angular disposition of the spindle is very slight, no attempt has been made to indicate the same in the figures illustrating the construction of the machine, as to do so would be impi'acticable. In Fig. 13, however, I have diagrammatically illustrated the preferred manner of disposing the spindle for the cutting of tapered threads` and reference may be had thereto for a better understanding thereof. In this ligure the threading cutter T is shown with a greatly exaggerated taper and the pipe P is shown as it would appear after being traversed by the threading cutter, assuming the saine were not provided with teeth. The axis of the spindle is designated by the broken line A-B which, it will benoted, is parallel to the line of contact between the cutter and the pipe while the axis X-X of the arbor 7 -on which the cutter i3 mounted and the axis of the pipe Y-Y are parallel. When the parts are arranged in this manner in an operative machine, it will be apparent that as the spindle progressively advances or moves to the right (Fig. 13) the end of the pipe will be gradually raised toward the cutter so that no matter how far the movement of the spindle is carried, the roper relation between the cutter and the plpe for the production of a erfect thread will always be maintained.) Such, however, would not be the case if the axes of the spindle and cutter were arallel, for under such conditions a3 the spindle advanced the pipe would gradually recede from the cutter and thereby prevent the latter from cutting to the required depth. Obviously, the desired result could be attained with equal facility in a machine designed so that the pipe is moved longitudinally to the left during the cutting operation, in which case, of course, the inclination of the spindle would result in a gradual lowering of the end of the pipe with respect to the cutter:

It will be apparent, however, as the ipe and the spindle respectively rotate a out relatively inclined axes, it is requisite, in order to maintain the pipe in proper contact with the cutter, to provide for a slight unlversal movement between the spindle and the pipe, which result is convenientlyobtained by the means hitherto described whereby the pi is secured in operatively fixed relation with the ball 76 which in turn is capable of slight universal movement with respect to the spindle.

Operation.

In :forming a tapered thread upon a pipe or other hollow, substantially cylindrical article in accordance with my improved method and by means of a machine of the general character of that hereinbefore described, the machine is initially so adjusted as to bring the table to the forward end of its path and the threading and roughing cutters into the same vertical plane but not into vertical alignment, the roughing cntter being dis osed below and considerably in the rear o the threading cutter and tbe cam 39 being in a position in which the roughing cutter supporting block is retracted toward the rear of the machine. The chuck for holding the pipe having been in serted into and clamped in the end thereof in such manner that the nose of the inember SS extends for a suitable distance he- -vom] the end of the pipe, the latter, with its opposite end supported on a suitable track or in any other cpuvenient way so that the pipe can be frei-ly rotated, is brought to the machine and disposed in a substantially horizontal position with the nose of member 88 against the centering point of the center S1, pins 92 being held in retracted position by suitable disposition of the collar 93. The latter is then rotated so as to force the pins into the groove 91 and draw the chuck firmly against the center and lock it thereto, the dog 98 meanwhile having entered hetween two of the adjacent lugs 99 on the end of the carrier of the chuck, thus placing the several parts ol the machine and the pipe in substantially the positions shown in Figs.

1 and 2 with spindle 25 retracted with shoulder 111 snugly seated against the adjacent face of the housing 24 and both cutters out of contact with the pipe. The table 4 having been adjusted to bring the pipe to the proper height with 'respect to the threading cutter and the roughing cutter set so that it will cut into the pipe for the desired depth, power is supplie to the machine, thereby causing rotation of both the arbor 7 carilyin the threading cutter and the main sha t 2% with resulti rotation of cani 39, roughing cutter, s ind c 25 (with corresponding rotatio'n of t ie pipe) and nut 112, the movement of the latter being effective through the train comprising gears 124, 119, 114 and l113 to r0- tate the nut 112. Cani 39 is so designed as to quickly move the roughing cutter support ing block forward thus carrying the roughing cutter into the rotatin pipe for the maximum de th of the roug ing cut, and to thereafter hold the roughing cutter supporting block in such advanced position, so that after the initial forward movement of the block is etfected and the cutter brought to depth, the distance between the axis of the cutter and the axis of rotation of the pipe remains constant until the entire surface of the pipe has passed beneath the cutter when the cam o rates to retract the block and the cutter to initial or starting position. Preferably, the roughing cutter and the pipe are arranged to revolve in the same direction which is such that as the pipe rotates thepoint at which the roiighing cut was commenced gradually moves upward so as to approach the threading cutter. Meanwhile, rotation of cam 39 has brought dog 63 into contact with linger 64, thus urging the trip rod 29 y forward to engage and actnate finger 14 and cause the latter to throw the automatic feed of the table 4 into operation, thereby causing the table with its attached mechanism to move rearward so as to carry the continuously rototing pipe toward the threading cuter. As the pipe is gradually carried against the eutter in the manner described, the latter `finally attains the requisite depth of cut to forni the threads and I prefer to so adjust the machine that this condition will be brought about when the axes of the pipe and cutter are in substantial vertical eligi- `the table, actuates t ment. Furthermore, the several relative movements of the cutters and the pipe to which I have 'ust referred are so timed with respect to each other, and the relative positions of the cutters and pipe are such, that the pipe is caused to rotate through an angle of substantially 90 following the commencement of the roughing cut before the threading cutter reaches its maximum depth, with the result that this cutter commences and continues its operation throughout the threading cycle on a surface from which the scale has been removed, which has been ta# pered in accordance with the taper of the thread to be formed, and which has been brought to truly circular cross sectional contour by the action of the roughing cutter, so that the threading cutter is relieved from any duty other than that of cutting the threads in the clean metal which has bren exposed by the roughing cut.

As soon as the table 4 has been moved rearward by the automatic feed for a sufficient distance to bring the threading cutter in to de th, a condition, which, as stated, will prefrably be brought about when the axes of the pipe and of the cutter are in substantial vertical alignment, a suitable stop 150, operatively fixed with respect to e trip 14 so as to disengage the feed and arrest further rearward movement of .the.table, which subsequently remains at rest until the pipe has completed a little more than a full revolution with respect to the threading cutter so that the latter is accorded an opportunity to operate on the entire surface to be threaded. Theoretically, a single complete revolution of the pipe with respect t this `cutter would be effective for this result, but in practice it is desirable to give the pipe slightly more than a full revolution with respect thereto in order to prevent any unevenness or inequalities in the thread segments at the points of juncture between those portions formed by the initial o eration of the cutter and those formed b t e final operation, and, in practice, revo ution of the pipe through an arc of 5 to 10 will ordinarily be sufficient for this purpose.

Additionally, since the pipe begins to revolve andthe roughing cutter commences its cut considerably in advance of the time when the threading cutter is brought to depth at a point already traversed by the former cutter, itis requisite, in order to permit the action of the threading cutter on the entire surface to be threaded, to impart to the pipe sufficient additional rotation be ond that actually required for the operation of the threadingr cutter to compensate for the time that the threading cutter was inoperative after the revolution of the pipe began, and as the angle between lines drawn to the center of the pipe from the centers of both preferabl cutters when the latter are in to depth is substantially the required additions. rotation is Substantially similar in amount. Thus, to enable both cutters to properly perform their respective functions, it is requisite to revolve the pipe, after the roughing cutter has been brought to depth, for a complete revolution or 360, plus 90, plus the slight amount desirable for insuring perfect joining of the thread segments, or approximately 455 to 460 in all, and it will f thus be ap arent that during the total revolution of t ie pipe the threading cutter will not be completely operative durlng approximately the first quarter revolution 0f the pipe and that the roughing cutter will be inoperative during approximately the final quarter revolution thereof.

The sequence of operations and relative position of the cutters and the pipe through the threading cycle are diagrammatically illustrated in Figs. 12* to 12f inclusive; Fig. 12lshowing the relative position of the cutters and pipe at the start of the cycle; Fig. 12b their position after the roughing cutter has been moved in to depth; Fie'. 12 their position after the pipe and rougliing cutter have been translated so as to brlng the threading cutter to its maximum depth of cut in the surface theretofore traversed by the roughing cutter; Fig. 12d their relative position after the roughing cutter has traversed substantially the entire surface of the pipe and the threading cutter has traversed approximately threeuarters of its surface, and Fig. 12 thelr relative position at the completion of the threading operation and Fig. 12' their position after retraction of the roughing cutter but before return of the table 4. It will be noted from an inspection of these figures that as the threading cutter is arranged to take a cut slightly deeper than that which would theoretically be required for the production of the threads,

the tops of the finished threads are'formedA a little below the surface produced by the roughing cut, so that during the final quarter revolution of the pipe the roughing cutter is entirely out of contact therewith and there is no possibility of the tops of the finished threads being blunted or otherwise damaged by contact with the roughing cutter as they pass beneath it.

It will be noted that While the roughing cutter is fed into the Work in a substantially radial direction with respect thereto, the

threading cutter, on the contrary, enters the work in a substantially tangential direction, and herein hes an important advantage of myinveutom for it has been found in practice that it is extremely difficult to consecutively feed a milling cutter readily into a plurality of pieces of work for exactly the i same distance each time. Moreover, the error so caused is doubled in the finished p1ece when the entire surface of the work is traversed by the cutter, as when a thread is being formed, so that, for example, if the cutter is fed in radially for .001 too far, the diameter of the finished piece will be .002 too small, or .002" too large if the cutter is fed in .001 short of the proper distance. In accordance with my invention, however, in which the work is fed to the cutter or the cutter to the work in a generally tangential as opposed tc a radial dlrect'ion, a relatively larve error in the length ofthe feed required to bring the cutter to depth, that is, in the distance through which the work or cutter is Imoved in the generally tangential direction, is not transmitted directly to the work with resulting direct diminution of the Iadius thereof in a corresponding amount, but merely -appears in the work in a very much smaller amount. Thus, in practice, assuming that the vertical distance between the axis of rotation of the pipe and the axis of rotation of the cutter is correctly d termined and the machine initially set to tha distance by pro er vertical adjustment of the table, a relatively large error, plus or minus, in feeding the pipe against the cutter (which may easily result from wear or imperfections in the table feeding means or from other causes) will not materially affect the diameter of the finished work as the increase or decrease in the length of the radius thereof which results from such an error is infinitely small compared with the amount of the error itself.

At the initiation of the threading cycle the spindle 25 is positioned with the, shoulder 111 abutting the face of the housing 24 and during the cycle is progressively ad'- vanced from such position through coat-tion of nut 112 with the master thread on the spindle so as to corresponda ly move the pipe longitudinally toward te left when viewed as in Fig. 2, and as the longitudinal progression of the pipe for each complete revolution is, as previously explained, equal to the pitch ofthe thread to be formed, the threading cutter, instead of merely forming a plurality of adjacent grooves in the pipe in planes normal to its axis, is effective to produce on the pipe in a single complete revolution thereof with respect to the cutter, a continuous spiral thread of a taper correspondin to t at of the cutter and of a length etermined b the effective length of the cutter. Itwill observed that as, following the completion of each threading operation, tlie return mechanism for the s iridle is effective to snuglyseat the sliou der 111 against the housing 24,' any lost motion between the master thread and the nut, or at other points of the mechanism, is taken up before the spindle starts to rotate and move from starting position in the ensuing cycle, so that before the cutters come into action on the pipe the various parts and particularl the master thread and the nut are snugly rought together and coordinated for accurate operation, and further that as each time the spindle is returned to exactly the saine starting position, the threading operation is commenced each time at the saine point on consecutive pieces of work.

It will be further observed that by reason olf the slightly angular disposition of the axis of the s indle with respect to the axis of the threa ing cutter, the pipe as it is rotated andinoved longitudinally is simultaneously gradually moved toward the axis of the cutter as the spindle advances, thus compensatin for the difference in radial inagnitude o the thread segments of the tapered thread which is being formed and preserving at all times during the cutting operation the proper relative positions of the cutter and of the work necessary for the production of a perfect thread of that character. It will be understood, however, that if the machine is designed for cutting straight threads instead of tapered threads such comi pensation is not required as the radial magnitude of all of the thread segments in the straight thread is the same, and therefore a machine intended for such purpose would ordinarily be so constructed so that the axes of the spindle and of the threading cutter are parallel in which case the longitudinal and rotative movements of the spindle during the threading operation will result solely in corresponding movements of the pipe.

Upon the completion of the several operations to which reference has been made and the pi e having thus been completely threaded, t e power is thrown oit of the machine so that-all parts will be brought to rest with the table 4 at the extremity of its rearward movement. The collar 93 is then loosened and the pipe, carrying the chuck, withdrawn from the machine, the spindle of course remaining in its advanced position. The operator, by means of the hand wheel 13 or other means provided, then operates the quick return feed so as to move the table forward to its initial or starting position during which movement the trigger 135 engafges the stop 136 so as to swing the level' 12S orward about its ivot substantially to the position shown in ig. 11 which is eil'ective to cause the pawl 119 to rotate the ratchet collar 117 and, in turn, to rotate the gears 114 and 113 with consequent rotation of the nut 112 in the saine direction as that in which it was driven' while the pipe was being threaded. Since the main arbor 7 is now stationary, the main drive shaft 27 is also stationary and the gear 100 prevented from rotation, so that as the master nut is turned (and being, as it is, incapable of longitudinal Amovement between the housings 24 and 74) the spindle, sliding through the gears loo 124 and 100, is retracted until the shoulder 111 contacts with the face of the housing 24, thus arresting further movement of the spindle. y Y

As it is desirable to insure the complete and sitive return' of the spindle to initial ypositlon each time that the mechanism functions, the throw of the trigger 135 is preferably so calculated as to move lever 128 forward in excess of the distance necessary to turn nut 112 the required amount to return the spindle, and the arts so arranged u through the medium of t e yielding connection between the levexwand link that when the lever has moved forward enough to bring shoulder 111 against the housing 24, 'the rod 132 thereafter merely slides through the block against the reslstance of spring 133 until the point of the trigger clears sto 136 when springs 133 and 134 immediate y respective y expand and contract so as to again 4 move the lever rearward and causeI the pawl to ride over the teeth of the ratchet to assume its normal position as in Figs. 1 and 3, as hitherto explained.

The length of the arc through which the nut 112 must turn to return the spindle to starting position of course will vary with the pitch'of the master thread and the longitudinal distance through which the s indle is 'moved during the threading cycle, ut generally speaking the nut will, for this pur# ose, be turned through an arc-approximatey e ual to the diiference between 360 and necessary the e rees of arc through which it has been turne for each revolution of the spindle, multiplied bythe total number of com lete revolutions and fractions thereof which ave been made by the spindle in its forward progression. Or, in other words, if for each revolution of the spindle, the nut has been turned for nine-tenths of a revolution as the indle has moved forward, thereturn of t e spindle can be accomplished by movin the nut in the same direction one-tenth o the total number of degrees through which the spindle has turned; thus, for example,

'using a master screw of one pitch to the inch and cutting a ten pitch thread on the 'ipe in a `machine such as herein descri 1t is for returning the spindle to rotate the nut substantially onetenth of 455 to 460 if that be the total number of degrees through which the spindle is turnedv during its forward movement. However, in ractical operation, the exact calculation o the arc throughv which-the nutvmust be turned is not required provided the means employed therefor are s o' designed and adjusted, preferably in the manner herein described, as to turn the nut for at least the required amount and thereafter absorb any excess motion of the parts without injury. thereto.

After the table, b means of the quick return feed, has been rought to starting position and the spindle aise returned to such ositio'n the machine is ,once more in con- 'tion for operation on another piece of pipe, cam 39 having already moved the roughing cutter supporting block and roughing cutter rearward to starting positien, prefcrabl immediately after the roughmg cutterA as completed lts work upon the pipe andA before the completion of the work of the threading cutter thereon.

While I. have illustrated in the accom-"-K panyin g drawin and have herein described with considerab e particularity one 'form of machine which I prefer;A to use in the performance of my improved method of milling threads, it is to bek understood that changes and modifications in the desi construction and arrangement of the e ements thereof may be made if4 desired for the purose of adaptin the machine for use under il'erent operatlve conditions and with differentclasses of work and further that the use of the machine is in no way limited to the millin of tapered threads on pipe Aas it may readi be employed in the performance of other nnllin operationslon other sorts of causing a roughing cutter to enter the work..

in a direction enerally radial to the work to eiect a roug ing cut therein, then causing a rotatable threading cutter to enter the work at a point therein previously traversed by the roughing cutter and in -a direction generally tangential to the work for a depth suilicienttto form a finished thread, and then operatin both cutters in the rotating work until eac has performed a complete circuit thereof.

2. The .method of milling threads which comprises the steps of rotating the work, brinng a cutter to a position to eil'ect a roug ing cut of ldesired depth therein, and then causing a threading cutter .to enter the workin a du'ection enerallyv tangential with respect thereto an at a point previously traversed by the first cutter.

3. The method of milling threads which comprises the ste s of rotating the work, brin g a rou l dept in the wor by causin relative move ment of the cutter and wor in a direction nerally` radial to the latter,l 4and then rin -ng a threading cutter to o' rative dept in the work at a point alrea y traversed by the roughing-cutterby causing rela* tire movement of the heating cutter and the work in a direction generally tangential to the surface of the latter.

4. The method of milling threads which comprises the steps 0f rotating the Work, bringing a roughing cutter radially into the work and then bringing a threading cutter to operative depth in the work by causing relative movement between the work and said cutter in a direction generally tangen-v tial to the Work.

5. The method of milling threads 'which comprises the steps of rotating the work, moving a rcughing cutter radially into the work, causing this cutter to traverse a portion of the surface of the work, and then bringing a threading ,cutter to operative depth in the work at a point theretofo-re traversed by the roughing cutter by e'ecting relative movement between the work and the threading cutter in a direction substantially arallel to the direction in which the roughing cutter was moved to bring it to depth in the work.

6. The method of milling threads which comprises the steps of rotating the work, bringing a roughing cutter to operative depth in the work in a direction substantially radial thereto, and then causing a threading cutter to enter the work in a direction substantially tangential thereto by effecting relative movement between the threading cutter and the Work while maintaining a fixed relationbetween the axes of the roughing cutter and of the work.

7. The method of milling .threads which comprises the ste `of rotating the work, bringing a roug ing cutter to y operative depth in the work in a direction substantially radial thereto, and then im arting a movement of translation to the wor and the roughing cutter as a unit and while the roughing cutter is operating upon the work so as to enga the workwith a threading cutter at a point previously traversed by the roughing cutter.

8. The method of milling threads which comprises the steps of rotating the work, moving a roughing cutter to o erative depth in the work in adirectionlsu stantially radial thereto, and then im artng a movement of translation to the wor and' the roughing cutter as a unit to cause a threading cutter to progressively enter the work to operative depth in a direction generally tangential -to the surface of the work at a point previously traversed bythe roughing cutter and while the latter is operating at another point in the Work.`

9. The method of milling threads which comprises the ste of rotating the work, bringing a ro 'n cutter. to operative depth in the wor an then causing a threadin vcutter to enter the work in a direction su stantially tangential thereto by electing relative movement between the threading cutter and the work While maintaining a substantially fixed relation between the axes of the roughing cutter und of the work.

10. In a machine for millin threads, the combination of means for holgding and roiating the work, a roughing cutter, a threading cutter, means for bringing the roughing cutter to depth in the work. and means for causing relative movement between the threading cutter and the work whereby the threading cutter may be caused to enter the work in u direction generally tangential thereto.

ll. In a machine for milling threads the `combination of means for holding and rototing the work, a roughing cutter, a threading cutter, means for bringing the roughng cutter to depth in the work, and means for moving the work against the threadiu(y cutter to cause the latter to enter the wor in a generalljs1 tangential direction While the roughing cutter is operating on the work.

19,. In a. machine for milling threads the y combination of means for holding an rotating the work, a roughing cutter, a threading cutter, means for moving the roughing cutter to depth in the work, means for effecting relative movement between the threading cutter to cause the latter to enga the work at a point theretofore traversed y the threading cutter, and means for imparting to the work simultaneously with its movement of rotation a longitudinal movement ot progression with respect to the threading cutter.

13. In a machine. for milling threads, the combination of means for holding and rotating the work, a roughing cutter, a threading cutter, means for movmg the roughing cutter to depth in the work, means for effecting relative movement between the threading cutter and the work to cause the threading cutter to engage the work at a point theretofore traversed by the roughing cutter, and means for imparting to the work a longitudinal movement of progression with respect to the threading cutter and a gradual movement in a direction generally transverse to the axis of rotation of that cutter simultaneously with the rotation of the work.

14. A machine of the class described comprising a Lthreading, cutter, a table movable with respect thereto, means for reciprocating the table, means 4for supporting and rotating the work to be threaded and movable with the table, aroughing cutter suported from the table. means vfor moving he roughing cut-ter relatively Ato the table and to said work supporting and rotating means, and means for driving both cutters.

15. A machine of the class described, comprising a threadingcutter mounted for rotation on a fixed axis, a table movable with 

